There are many manufacturing methods of making white light emitting diodes (WLEDs), such as applying yellow phosphors to a blue light-emitting diode chip, applying red and green phosphors to a blue light-emitting diode chip, mixing red, green, and blue light-emitting diode chips and applying tricolor blue/green/red phosphors or applying different phosphors with different colors to a light-emitting diode emitting in the UV spectral range.
Compared to a traditional incandescent light bulb, a white light-emitting diode has some advantages, e.g. long lifetime, low power consumption, small volume, fast response time and good shake-resistance, and thus light-emitting diodes are gradually replacing traditional lighting products. However, current white light emitting diodes still need to overcome the problems such as heat dissipation, inadequate brightness and relatively high price in its development. As a result, in the lighting market, auxiliary lighting, including flash lights, car interior lights, architectural decorative lighting products, is still the main market of white light-emitting diodes, while still white light-emitting diodes are expected to replace traditional lighting products in the future to become the mainstream of the global lighting market.
Besides package techniques, the chosen phosphor is also an important factor in affecting luminous efficiency of a light source. Thus, one of the research directions that solid state lighting companies are devoted to is modifying phosphor compositions to increase phosphor conversion efficiency. The color render index of the white light generated by a yellow phosphor excited by a traditional single blue chip is not good and thus the color saturation of an object illuminated by such white light is poor, thereby lowering the commercial lighting market value. After many years of research and development, it is found that using a high efficient UV-light-emitting diode (UV-LED) as an excitation light source is another way of white light emitting diodes to become lighting devices. Because the UV-LED technique is gradually mature, the phosphor development of the UV-LED excitation light source is more and more important, so as to develop phosphors matching the emission wavelength of UV-LEDs and thus manufacture white light emitting diodes with high efficiency and high brightness.